This invention is directed to a metal etching process involving contacting a metal with an etching solution containing a metal ion or a complex ion in a first valence state which is reduced to a lower valence state, resulting in oxidizing the metal being etched, thereby forming a metal ion which goes into the solution. More specifically, the invention relates to a process for etching metals that normally have slow etch rates, which process greatly enhances the etch rate of the metals, and provides for rejuvenation of the etching solution.
The general concept of etching metals, particularly copper, with an etchant solution containing an ion in a first valence state that is reduced to a lower valence state by an oxidizing reaction with copper, and forming an ion, is well known and widely used. The process applied to etching copper with ferric chloride solutions is described in U.S. Pat. No. 1,969,678. Various techniques to rejuvenate the etching solution by oxidizing the oxidizing ion in solution back to the original first valence state is well known, as indicated by U.S. Pat. Nos. 2,886,420, 3,600,244, and 3,532,568.
Normally, the etching of copper by such processes proceeds at an acceptable rapid etching rate, particularly with ferric chloride solutions. However, the etching of other metals, for example, nickel, proceeds at an unacceptably slow rate, even though the oxidation potentials for the reactions are thermodynamically favorable. The kinetics of the reaction are intolerably slow for various reasons, some of which are not completely understood. Conceivably some product of an intermediate reaction blocks the metal surface and impedes the overall etching reaction. Agitation from of solution results in only a minor improvement.